White tights can work, cut them at the top just under the crotch. If you keep the differently woven part at the top they won't unravel. Usually being rolled inside the pants will keep them up, if not a little bit of ribbon or something like that tied, with the excess tight rolled down, will be enough to keep it from falling down.
If we can't find anything to work locally then we can make a group order online for the show, and I can find something that will work.
Nobody sweat tomorrow too much, it's meant to be fun, and as far as costumes it's a good reminder of what all we still need to get.